Process for preparation of polyester polyols utilizing polyalkylene terephthalate

Abstract

The process of the present invention reacts a polyhydric alcohol and a second reactant selected from the group consisting of polycarboxylic acid, anhydride or an ester of a polycarboxylic acid in a first reactor to produce a flowable intermediate ester. During this reaction, volatile by-product is removed. The flowable intermediate ester is transferred to a holding vessel from which it is metered to a second reactor. Additional polyhydric alcohol may be added to the flowable intermediate ester which may be preheated by heat exchange with the finished polyester before introduction to the second reactor. A polyalkylene terephthalate feed is introduced to the second reactor in which it is reacted to form a finished polyester which is continuously removed from the second reactor. By altering the feeds to the second reactor, the physical characteristics of the finished polyester may be changed to meet various specifications.

What is claimed is: 
     
       1. A process for the preparation of a polyester polyol, comprising the steps of: (a) reacting in a first reactor a polyhydric alcohol and a second reactant selected from the group consisting of a polycarboxylic acid, anhydride or an ester of a polycarboxylic acid at a first temperature with removal of a volatile by-product until a flowable intermediate ester has been produced;   (b) transferring the intermediate ester to a holding vessel in which it is held in a flowable condition;   (c) metering the intermediate ester to a second reactor;   (d) metering a recycled polyalkylene terephthalate feed to the second reactor; and   (e) reacting the intermediate ester with the polyalkylene terephthalate feed at a second temperature to form a finished polyester which is continuously removed from the second reactor.   
     
     
       2. A process as recited in claim 1 wherein the polyhydric alcohol is initially used to charge the first reactor, the polyhydric alcohol is then heated to a temperature between about 140° C. and about 240° C. and the second reactant is then added to the first reactor. 
     
     
       3. A process as recited in claim 2 wherein an additional amount of polyhydric alcohol is added to the first reactor after the second reactant has been added to said first reactor. 
     
     
       4. A process as recited in claim 3 wherein substantially all of the volatile by-product generated by the addition of the second reactant is removed before the additional amount of polyhydric alcohol is added to the first reactor. 
     
     
       5. A process as recited in claim 1 wherein the polyhydric alcohol is comprised of diethylene glycol and the second reactant is comprised of phthalic anhydride. 
     
     
       6. A process as recited in claim 1 wherein the second temperature is maintained between about 220° C. to about 240° C. 
     
     
       7. A process as recited in claim 1 wherein the flowable intermediate ester has an acid number less than about 5. 
     
     
       8. A process as recited in claim 1 wherein the intermediate ester is preheated before being passed to the second reactor by heat exchange relationship with the finished polyester. 
     
     
       9. A process as recited in claim 1 wherein a catalyst is added to the first reactor. 
     
     
       10. A process as recited in claim 1 comprising the further steps of cooling the flowable intermediate ester and then adding a catalyst to the flowable intermediate ester before said intermediate ester is transferred to the holding vessel. 
     
     
       11. A process as recited in claim 1 wherein the polyalkylene terephthalate feed is metered into the second reactor in a solid state which is dissolved in said second reactor in less than about one hour. 
     
     
       12. A process as recited in claim 1 or 11 wherein the second reactor has an average residence time of less than about six hours. 
     
     
       13. A process as recited in claim 12 wherein the approximate weight ratio of polyalkylene terephthalate feed to the flowable intermediate ester is greater than 1:2. 
     
     
       14. A process as recited in claim 1 wherein the yield of the finished polyester is in excess of about 98%. 
     
     
       15. A process as recited in claim 1 wherein the second reactor is maintained at a substantially constant volume during continuous operation. 
     
     
       16. A process as recited in claim 1 wherein steps (a) and (b) are repeated and steps (c) through (e) are continuous. 
     
     
       17. A process as recited in claim 1 wherein the intermediate ester is metered into a bottom half of the second reactor, the polyalkylene terephthalate feed is metered into a top half of the second reactor and the finished polyester is removed from the top half of the second reactor to create a mixing effect which helps to dissolve the polyalkylene terephthalate feed which settles into the bottom half of said second reactor. 
     
     
       18. A process as recited in claim 1 wherein an overhead stream consisting primarily of glycols is removed from the second reactor. 
     
     
       19. A process for the preparation of a polyester polyol, comprising the steps of: (a) charging a first reactor with a first amount of polyhydric alcohol and a second reactant selected from the group consisting of a polycarboxylic acid, anhydride or an ester of a polycarboxylic acid;   (b) heating the polyhydric alcohol and the second reactant in the first reactor to a first temperature;   (c) removing substantially all of a volatile by-product from the first reactor;   (d) transferring a flowable intermediate ester formed in the first reactor to a holding vessel;   (e) passing the intermediate ester through a heater to a second reactor;   (f) metering a recycled polyalkylene terephthalate feed to the second reactor;   (g) reacting the intermediate ester with the polyalkylene terephthalate feed to form a finished polyester with a predetermined set of physical characteristics; and   (h) continuously passing the intermediate ester from the second reactor.   
     
     
       20. A process as recited in claim 19 wherein the heater is comprised of a heat exchanger through which the intermediate ester is passed. 
     
     
       21. A process as recited in claim 19 wherein steps (a) through (d) are repeated. 
     
     
       22. A process as recited in claim 19 wherein the polyhydric alcohol is comprised of diethylene glycol and the second reactant is comprised of phthalic anhydride. 
     
     
       23. A process as recited in claim 19 wherein the second temperature is maintained between about 220° C. to about 240° C. 
     
     
       24. A process as recited in claim 19 wherein the acid number is less than about 5. 
     
     
       25. A process as recited in claim 19 wherein a catalyst is added to the first reactor. 
     
     
       26. A process as recited in claim 19 comprising the further steps of cooling the flowable intermediate ester and then adding a catalyst to the flowable intermediate ester before said intermediate ester is transferred to the holding vessel. 
     
     
       27. A process as recited in claim 19 wherein the polyalkylene terephthalate feed is metered into the second reactor in a solid state which is dissolved in said second reactor in less than about one hour. 
     
     
       28. A process as recited in claim 19 or 27 wherein the second reactor has an average residence time of less than about six hours. 
     
     
       29. A process as recited in claim 19 or 27 wherein the approximate weight ratio of polyalkylene terephthalate feed to the flowable intermediate ester is greater than about 1:2. 
     
     
       30. A process as recited in claim 19 wherein the yield of the finished polyester is in excess of about 98%. 
     
     
       31. A process as recited in claim 19 wherein the second reactor is maintained at a substantially constant volume. 
     
     
       32. A process as recited in claim 19 wherein the intermediate ester is metered into a bottom half of the second reactor, the polyalkylene terephthalate feed is metered into a top half of the second reactor and said intermediate ester is removed from the top half of the second reactor to create a mixing effect which helps to dissolve the polyalkylene terephthalate feed which settles into the bottom half of said second reactor. 
     
     
       33. A process as recited in claim 22 wherein an overhead stream consisting essentially of water is removed from the second reactor. 
     
     
       34. A process for the preparation of a polyester polyol, comprising the steps of: (a) reacting in a first reactor a polyhydric alcohol and a second reactant selected from the group consisting of a polycarboxylic acid, anhydride or an ester of a polycarboxylic acid at a first temperature to from a volatile by-product and an intermediate flowable ester;   (b) removing substantially all of the volatile by-product;   (c) passing the intermediate ester from the first reactor to a holding vessel;   (d) combining a stream of polyhydric alcohol with a stream of intermediate ester from the holding vessel to form a continuous feed stream which is introduced to a second reactor;   (e) introducing a recycled polyalkylene terephthalate feed to the second reactor where it is reacted at a second temperature to form a finished product with a predetermined set of physical characteristics; and   (f) continuously passing the finished product from the second reactor.   
     
     
       35. A process as recited in claim 34 wherein the continuous feed stream is heated to the second temperature before it is introduced to the second reactor. 
     
     
       36. A process as recited in claim 35 wherein the continuous feed stream is heated by heat exchange with the finished product. 
     
     
       37. A process as recited in claim 34 wherein steps (a) through (c) are repeated. 
     
     
       38. A process as recited in claim 34 wherein the polyhydric alcohol is comprised of diethylene glycol and the second reactant is comprised of phthalic anhydride. 
     
     
       39. A process as recited in claim 34 wherein the second temperature is maintained between about 220° C. to about 240° C. 
     
     
       40. A process as recited in claim 34 wherein the acid number is less than about 5. 
     
     
       41. A process as recited in claim 34 wherein a catalyst is added to the first reactor. 
     
     
       42. A process as recited in claim 34 comprising the further steps of cooling the flowable intermediate ester and then adding a catalyst to the flowable intermediate ester before said intermediate ester is transferred to the holding vessel. 
     
     
       43. A process as recited in claim 34 wherein the polyalkylene terephthalate feed is introduced into the second reactor in a solid state which is dissolved in said second reactor in less than about one hour. 
     
     
       44. A process as recited in claim 34 or 43 wherein the second reactor has an average residence time of less than about six hours. 
     
     
       45. A process as recited in claim 44 wherein the approximate weight ratio of polyalkylene terephthalate feed to the flowable intermediate ester is greater than about 1:2. 
     
     
       46. A process as recited in claim 34 wherein the yield of the finished polyester is in excess of about 98%. 
     
     
       47. A process as recited in claim 34 wherein the second reactor is maintained at a substantially constant volume during continuous operation. 
     
     
       48. A process as recited in claim 34 or 47 wherein the intermediate ester is metered into a bottom half of the second reactor, the polyalkylene terephthalate feed is metered into a top half of the second reactor and said intermediate ester is removed from the top half of the second reactor to create a mixing effect which helps to dissolve the polyalkylene terephthalate feed which settles into the bottom half of said second reactor. 
     
     
       49. A process as recited in claim 34 wherein an overhead stream consisting essentially of water is removed from the second reactor. 
     
     
       50. A process as recited in claim 34 wherein the volumes of the stream of polyhydric alcohol, the stream of intermediate ester and the recycled polyalkylene terephthalate feed are adjusted to obtain the finished product with the predetermined set of physical characteristics. 
     
     
       51. A process as recited in claim 34 or 37 comprising the further steps of: (g) altering the volumes of at least one of the streams of polyhydric alcohol, the stream of intermediate ester or the recycled polyalkylene terephthalate feed to obtain a modified finished product with a new set of predetermined physical characteristics.   
     
     
       52. A process as recited in claim 51 wherein steps (a) through (c) are repeated after the modified finished product is obtained. 
     
     
       53. A process as recited in claim 51 wherein step (g) is repeated to obtain at least one new modified finished product. 
     
     
       54. A process as recited in claims 1, 19 or 34 wherein the second reactant is comprised of phthalic anhydride.